In general, Devonian rocks exposed north of a line from Bristol to London are of continental ‘Old Red Sandstone’ facies, while to the south a variety of marine facies predominate (Goldring et al. 1967; Selwood & Durrance 1982; Bluck et al. 1988) (Fig. 1). Thus, Devonian ostracods are mainly restricted to Devon and Cornwall, although there are records from marine horizons in South Wales. Little taxonomic work has been carried out on these faunas and only very general palaeoecological information is available. This reflects both the complex tectonic setting of the region (Selwood 1990; Selwood & Thomas 1987, 1988) and the often poor preservation of most of the ostracod material. Only with the establishment of a Late Devonian ostracod chronology in the Rheinish Slate Mountains of Germany (Rabien 1954; Krebs & Rabien 1964; Buggisch et al. 1978, 1986) have ostracods been used to resolve geological problems in Devon and Cornwall.